BA, ME, Metric Coarse or Imperial : which taps and dies to buy ?

[JasonBModerator @jasonb]

Yes if they don't give a pitch its regarded as Metric coarse so M4x0.7

Possibly missed the translation and put irons rather than dies although the sterling says dies

[AjohnwParticipant @ajohnw51620]

I don't think you really need metric fine generally Brian but it would be best to canvas opinions on that.

Personally if metric fine is ever needed I would buy them separately. Using the BA argument again M2 is close to 9BA which has a pitch of .391mm. BA is one of the most used standards on models especially at small thread sizes. At this sort of size 40 tpi is too coarse really.

However –

Looking on the pages for the John engine you want to build the ones where the pitch is specified may be metric fine not the others. This is fairly normal. With spec's like M2, M3 etc metric coarse can be assumed. If the pitch is specified it might even be none standard let alone metric fine. In this case M5x0.5 and M8x0.75 is needed. The reasons that it happens on larger sizes is usually down to scale. Threads might be visible but more often the size of the part concerned in some one's opinion is too small to have sufficient threads engaging if a normal pitch is used. The normal metric sizes would be M5x0.8 and M8x1.25. When other pitches are given they may or may not be metric fine. There has been a mad range of standard metric diameter and pitch arrangements. There still is but ISO have limited the pitches that can be used – they hope.

The screwfix set I mentioned has some unusual sizes in it. A coarser M5 and a finer M8 plus others.

If you are thinking about buying Arc's M1 to M2.5 set be careful with the smaller sizes. They can snap rather easily unless the tap is very well axially aligned with the hole it's going in.

The downside of cheaper sets is usually accuracy. In other words better quality ones MAY produce parts which will fit more closely together but very accurate ground thread taps and dies don't seem to exist any more. The dies generally cut undersized and taps over. In the past taps have been made exactly on size – where ever they come from now they always seem to be over.

John

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[JasonBModerator @jasonb]

John, on continental Europe they use metric fine and extra fine pitches on models like we use 32tpi ME and 40tpi ME for things like glands and pipe fittings as I mentioned above

[AjohnwParticipant @ajohnw51620]

I just tried to explain why this happens in general terms Jason and to explain why metric coarse is ok when that is used as in real terms it's close to BA – an instrumentation thread unless you are Colin Chapman and decide to use it to attach the rather long massive radius arms on the rear wheels of a Lotus Europa. That really caused me some grief once,

My immediate thought once metric became more popular was where are the metric model engineering threads ? As far as I am aware this is purely a UK invention, a very convenient one so looked for all of those 0.5mm pitch taps and dies or such like that would be needed. Then tried brass. No luck. I expected a search like this to bring something suitable up

**LINK**

Remove the set from the search and some metric fine will be found.

Perhaps the answer to the John engine for some one who had the cutters available would be to replace 5mm with 3/16 ME 40 and M8 with 5/16 same, 32tpi or brass. They are so close on diameter it makes me wonder if it's a metricated imperial design. The 3/16 is .010 low on diameter though.

Rule Britannia – seems to be the only country that took model engineering seriously.

John

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Edited By John W1 on 27/07/2015 20:38:53

[JasonBModerator @jasonb]

I did suggest he use his existing ME taps and dies at 10.20 this morning

[AjohnwParticipant @ajohnw51620]

Posted by JasonB on 27/07/2015 20:40:18:

I did suggest he use his existing ME taps and dies at 10.20 this morning

7 pages put me off back reading. Must be great minds think alike.

John

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[Another JohnSParticipant @anotherjohns]

Posted by JasonB on 27/07/2015 19:23:49:

John, on continental Europe they use metric fine and extra fine pitches on models like we use 32tpi ME and 40tpi ME for things like glands and pipe fittings as I mentioned above

That's how I became metricated – living in continental Europe. All of my fittings are metric, (metric fine, etc), as they make sense, and taps/dies are easier to get locally (Canada) than the "ME" sizes.

Same with BA – I use metric equivalents. Just my 0.02 cents canadian.

[Edgar Vin 1Participant @edgarvin1]

When the pipe spins do the jaws leave marks all along the pipe or just at the very bottom, this would indicate the jaw is lifting and not applying the same level of grip along the whole length of the pipe.

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